Unfortunately, it sounds like you have CG-NAT (Carrier Grade NAT) on your current network, other forum posts seem to indicate that this is common for EE:
If you would like, you can confirm directly with them to see if there’s any way you can enable proper port forwarding, or if not, some users have gotten ARC through a CG-NAT by using Tailscale, but this is not something we tested so we would be unable to advise specifics: